quick question about an increasing source of 12v as revs go up

[bzrmatt]

Hi,

First time poster and i'm not too knowledgeable about the auto electric side of things so go easy...

I've made a basic forced induction unit for my car, it's pretty much just a powerful 12v fan inside the air intake that I can switch on/off from within the car... It's a noticeable performance gain but it's getting a bit annoyin switchin it off and on.

My question is, Is there a + power source that I can tap off that increases voltage with revs, so that as the revs go higher the fan speed increases? and when idling the fan is either on low voltage or off. Also when the car is off the fan is off, like ignition power..?

My car is a 97 toyota trueno bz-r .

Thanks for any replies

[shorod]

Welcome to the forum!

For the amount of fan speed difference you're looking for, you really would need to make your own speed controller for the fan since the charging system voltage on a properly working charging system will not fluctuate enough to make a significant difference in the fan's rpms.

Probably the easiest approach would be to use a relay with the switched side of the relay connected to a constant 12V source through a fuse with pretty heavy gauge wire. Then control the coil of the relay with a circuit that is only active when the ignition switch is in the Run position (such as maybe the fuel pump circuit). Then use the Throttle Position Sensor (TPS) as your variable resistance in to a Pulse Width Modulated (PWM) speed controller with heatsinked high current MOSFET output transistors. For added life you could mount the heatsink in the air flow from the intake fan. Your PWM controller could be made from a simple 555 timer IC or the simplest solution could be to use a blower motor speed controller from a vehicle that has auto climate control. Ones like Ford uses in their 1996-2001 Explorers in the US should be in pretty large supply and already have provisions to be mounted in ductwork with air flow, and also can handle quite large amounts of current. You would probably need to scale the variable voltage level from the TPS sensor though, and I'm actually not sure if the blower motor speed controllers receive just a variable voltage input or if they receive a PWM signal and just provide the high current capability. A wiring diagram from the related service manual would be able to provide that information. If they required a PWM signal then the 555 timer as the PWM source would still be a good option.

But, you may also want to do some research on how effective (or maybe I should type ineffective) these types of systems really are before you go to all of this work. I certainly would suggest you don't make any permanent mods that cannot be undone your resale value may go down if a future prospective buyer opens the hood and sees some cobbled up "electric supercharger" installed in the intake system. The general consensus seems to be these block too much air flow, disturb the air path, load the engine (high current draw on alternator) and don't actually compress the air, therefore any "gains" are generally psychological rather than empirical. It could be a fun project to get to understand electronics a bit better, but that may be the only benefit from it.

-Rod

[handyman01]

this might help
http://www.youtube.com/watch?v=5UISZ...ature=youtu.be

[shorod]

Originally Posted by handyman01

this might help

How does that video have anything to do with the thread topic? And how does someone make it take over 11 minutes to change out windshield wipers?

-Rod

[MagicRat]

Originally Posted by bzrmatt

Hi,

First time poster and i'm not too knowledgeable about the auto electric side of things so go easy...

I've made a basic forced induction unit for my car, it's pretty much just a powerful 12v fan inside the air intake that I can switch on/off from within the car... It's a noticeable performance gain but it's getting a bit annoyin switchin it off and on.

My question is, Is there a + power source that I can tap off that increases voltage with revs, so that as the revs go higher the fan speed increases? and when idling the fan is either on low voltage or off. Also when the car is off the fan is off, like ignition power..?

My car is a 97 toyota trueno bz-r .

Thanks for any replies

Two issues:
1. Presumably, you do not need the boost in performance unless you actually go to full throttle. So, why stress your alternator by having the fan function all the time?
It may be easier to go with a simple electrical switch and relay hooked up to the gas pedal, where the switch is turned on when you push the pedal all the way to the floor.
You may be able to adapt the kickdown switch for an older General Motors car equipped with the THM 400 automatic transmission... this is most of the full-size GM cars from the 1970's. You would need a relay as well.

2. Can you post more details about your set-up? I was considering such a set up using a cordless 12 volt Black & Decker leaf blower hooked up to the intake on a smaller car. It flows at 400 cfm with enough pressure to move pebbles and gravel when blowing, (at least 2 or 3 PSI, my guess). I guess some one-way vacuum valves and a vacuum reservoir would be required so intake manifold pressure would not cause the vacuum to be lost for vacuum -operated devices.

[bzrmatt]

Hi and thanks for the responses, sorry bout the delay in reply..

@shorod
Cheers for the welcome and for the detailed response, I understand in a basic sense what you've described in all honesty it does sound like more trouble and cash than it's worth for the sorta performance gains i'm getting, It's good to know however that it would be possible to do this though if I were to make an upgraded version at some stage...

I agree with you in regards to the amount of work required versus how actually effective the system ends up being, however if there was a voltage somewhere that did have this characteristic it would probably be worthwhile for the small amount of wiring i'd have to do..

Currently the car has a rebuilt 1600cc 4age blacktop engine, the air intake system is custom, with the plenum going to a stainless steel pipe with a rubber joiner between that and the pod filter.. The fan is located in the rubber joiner and I have a spare one that hasn't been modified so it's pretty easy to switch those.

the general consensus sounds about right about blocking air flow, with the fan turned off, the airflow seems slightly restricted (than with no fan), but with the fan turned on it is the opposite and runs better than it would without it.. This is the whole reason i'd like it rpm based, so that, like you said, it would not be a constant draw from the alternator, nor a restriction when it's in low use etc etc which is probably about 95% of the time anyway..

... thanks handyman01

@magicrat

yes that's correct, however the last thing I would want would be the fan restricting the air flow for day to day use which is sorta why I'd like it to be operating low voltage for regular driving most of the time.. But that is a really awesome idea re the gas pedal switch and relay. Think I might give that a go, cheers

2. Can you post more details about your set-up?
Sure,
see above for how the air intake is setup.. I'm an IT technician by trade and always have an abundance of spare parts, including a lot of fans.. 99% are pretty weak but occasionally I come across ones about two inches thick with the fan shaped more like a turbine than a regular fan and a hell of a lot higher amperage (sorry i'd get the amps but it's in my car at the moment)
While in the computer they are limited to low speed most of the time, but removing the speed limiter wire and running them straight off 12v they spool up to full speed and are actually pretty scary to hold on to...
The one I used was square in shape, but I dremeled it into a circle, and epoxyd it inside a rubber pipe joiner.. It was almost a perfect fit

Interesting thought about the vacuum valves, reservoir etc, I haven't done anything like that,.. I don't know if my setup is enough to deem it worthwhile or if there is that much pressure being created or able to be utilised..

Thanks again for the replies